Fuel injection valve

ABSTRACT

A fuel swirler positioned upstream of an injection orifice is disposed at the tip of a nozzle body in a fuel injector, in which the fixed core and the nozzle body are coupled to each other via a non-magnetic cylindrical seal ring press-fitted and welded to the outer circumference of one end on the nozzle body side of the fixed core and the inner circumference of one end of the nozzle body. The inner circumference of the fuel swirler and the inner circumference of the seal ring function serve as a guide for slidably guiding a stroke movement of the needle. The fuel swirler is held between the receiving surface of the nozzle body and the orifice plate, thus defining an annular fuel passage between the outer circumference of the fuel swirler and the inner circumference of the nozzle body, so that fuel flows into a passage groove formed at the lower end surface of the fuel swirler via the annular fuel passage. A mass movable in an axial direction independently of the needle is interposed between the return spring and the needle, and a plate spring is interposed between the mass and the needle.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to an electromagnetic fuel injector(injection valve) for an internal combustion engine.

2. Background Art

There has been conventionally used an electromagnetic fuel injectorwhich is driven in response to an electric signal output from an enginecontrol unit in an internal combustion engine for an automobile or thelike.

This type of fuel injector is configured such that an electromagneticcoil and a yoke are arranged around a hollow cylindrical fixed core. Anda nozzle body containing a movable element (thereafter call “needle”)with a valve element is fixed to the lower portion of the yoke, so thatthe needle is urged toward a valve seat by the force of a return spring.

A two-point support guide system is generally used for the needle inorder to achieve the stability of a stroke movement. For example, asdisclosed in Japanese Patent Laid-Open No. Hei 11-200993, in the casewhere the movable element is a needle valve, the tip of the needle valveis slidably guided on the inner circumference of a fuel swirler housedinside a nozzle body. And as to another point, a large-diameter portionfunctioning as a guide surface on a movable side is formed in the needlevalve, to be thus slidably guided on the inner circumference of thenozzle body. A similar two-point support guide system is used for aneedle configured by integrally coupling a ball and a rod which serve asa valve element.

In recent years, a fuel injector for directly injecting fuel into acylinder in an internal combustion engine has been put to practical usealso in a gasoline engine.

In the direct injection type of fuel injector, there has been proposed along nozzle injector in which a nozzle body disposed under a yoke isslenderly elongated. In fixing such a long nozzle injector to a cylinderhead, only the slender nozzle body occupying little space is placed onthe cylinder head. And in the injector, a large-diameter body consistingof a yoke, a connector mold and the like can be provided apart fromother parts and the cylinder head without any interference. Therefore,in the case where parts such as a suction valve and a intake manifoldare densely disposed in the vicinity of the cylinder head, said fixingof the long nozzle injector has advantage of the high degree of fixingfreedom.

In the above-described two-point support guide system for the needle, itis necessary to finish (grind) a guide hole formed at the innercircumference of the nozzle body in the case where the stroke movementof the needle is guided on the inner circumference of the nozzle body.If the nozzle body is elongated, the guide surface is deeply positioned,thereby making machining difficult. In the meanwhile, even in the casewhere the guide surface is formed at the inner circumference near anopening of the nozzle body, followed by finishing, the innercircumference of the nozzle body requires a high grinding accuracy,thereby increasing a fabricating cost accordingly. Consequently, costreduction is desired.

In addition, since the valve element collides with a valve seat during avalve closing operation in the electromagnetic fuel injector, the valveis accidentally opened by a bounce of the valve element, therebyinducing a fear of so-called secondary injection. Therefore, there arevarious demands for the technique for preventing such secondaryinjection, the configuration which contributes to assemblingfacilitation, in particular, automatic assembling, and the like.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a fuel injector whichcan solve problems such as cost reduction, centering accuracy (coaxialaccuracy) and assembling facilitation of a fuel injector, simplicity ofcomponent parts, the degree of fixing freedom, and prevention ofsecondary injection.

The present invention has been proposed to attain the above-describedobject by way of a variety of modes. The gist of the present inventionis as follows:

An electromagnetic fuel injector is basically configured such that anelectromagnetic coil and a yoke are arranged around a fixed core, anozzle body containing therein a needle with a valve element is fixed tothe lower portion of the yoke, and the needle is urged toward a valveseat with application of the force of a return spring, and further, isprovided with the following means:

(1) In order to achieve the cost reduction and centering accuracy(coaxial accuracy) in the two-point support guide system, a two-pointsupport guide is composed as follow. In a fuel injector having the fuelswirler, a two-point support for slidably guiding a needle on the innercircumference of a non-magnetic cylindrical seal ring and the innercircumference of a fuel swirler during a valve stroke movement iscomposed by using the seal ring press-fitted and welded to the outercircumference of one end on a nozzle body side in a fixed core and theinner circumference of one end on the nozzle body side.

(2) In order to facilitate the assembling work of the fuel injector andsimplify component parts, an electromagnetic coil and a yoke areinserted from above the fixed core, and thus, are disposed around thefixed core. Furthermore, the yoke is configured such that it can becoupled to the nozzle body in such a manner as to cover the outerperiphery of an electromagnetic core. A terminal taking-out window forthe electromagnetic coil is formed at a part of the upper portion of theyoke. The inner surface of the upper end of the yoke is pressed againstthe electromagnetic coil, thereby fixing the coil.

(4) Means described below are proposed to facilitate the assembling workof the fuel swirler and enhance the characteristics and responsivenessof fuel injection:

The fuel swirler is loosely fitted to the inner circumference of thenozzle body in such a manner as to be received by the receiving surfaceof the nozzle body. An orifice plate is press-fitted to the innercircumference in such a manner as to press the fuel swirler. Consideringthis from different points of view, the configuration is proposed thatthe fuel swirler is held between the receiving surface of the nozzlebody and the orifice plate, and thus, an annular fuel passage is definedbetween the outer circumference of the fuel swirler and the innercircumference of the nozzle body, so that fuel flows in a passage grooveformed at the lower-end of the fuel swirler via the annular fuelpassage.

(5) In order to prevent any secondary injection, means described beloware proposed as the composition capable of implementing a liquid damperstructure for alleviating an impact occurring during a valve closing ofthe needle.

The inner circumference of the seal ring extending over the outercircumference of one end on the nozzle body side in the fixed core andthe inner circumference of one end on the nozzle body side serves as aguide for the needle. The needle includes a hollow, cylindrical movablecore. The outer circumference of the upper portion of the movable coreis guided on the inner circumference of the seal ring. The fuel passageis secured between the outer circumference of the lower portion of themovable core and the inner circumference of the nozzle body. The fuelpassage communicates with another fuel passage defined inside of themovable core upstream thereof via a through hole formed at the movablecore.

(6) As means for preventing any collision (a bounce) of the needleagainst a valve seat or a stopper in order to prevent any secondaryinjection, there are proposed that an axially movable mass independentlyof the needle is interposed between the return spring and the needle,and that a plate spring is interposed between the mass and the needle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view showing a fuel injector in apreferred embodiment according to the present invention;

FIG. 2 illustrates the mounted state of the fuel injector;

FIG. 3 illustrates the assembling process of the fuel injector;

FIG. 4( a) is a top view showing a fuel swirler to be used in thepresent embodiment, FIG. 4( b) is a bottom view of the fuel swirler, andFIG. 4( c) is a vertical cross-sectional view of the fuel swirler; and

FIG. 5( a) is a plan view showing a damper plate (a plate spring) to beused in the present embodiment, and FIG. 5( b) is a cross-sectional viewshowing the damper plate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A best mode embodying the present invention will be described inreference to a preferred embodiment shown in FIGS. 1 to 5.

As shown in FIG. 1, a hollow fixed core 1, an electromagnetic coil 2 anda yoke 4 are arranged from the center toward the outer diameter in afuel injector 100, and further, a needle 5 with a valve element iscontained inside a nozzle body (also referred to as a nozzle holder) 18fixed to the lower portion of the yoke 4, wherein the needle 5 is urgedtoward a valve seat 31 by the force of a return spring 7.

With respect to the basic movement of the fuel injector 100, when theelectromagnetic coil 2 is energized, the yoke 4, the fixed core 1, amovable core 14, (i.e., a part of the needle 5) and the upper portion ofthe nozzle body 18 constitute a magnetic circuit, so that the needle 5is attracted against the force of the return spring 7, thereby achievinga valve opening; in contrast, when the energization of theelectromagnetic coil 2 is stopped, the needle 5 abuts against the valveseat 31 by the force of the return spring 7, thereby achieving a valveclosing.

In the present embodiment, the lower end of the fixed core 1 functionsas a stopper for receiving the needle 5 during the valve opening.

The fixed core 1 is formed into an elongated, hollow and slenderlycylindrical shape. The fixed core 1 and the nozzle body 18 are coupledto each other via a non-magnetic, cylindrical seal ring 8 extending overthe outer circumference of one end on the nozzle body side of the fixedcore 1 and the inner circumference of one end of the nozzle body 18.

The seal ring 8 is ground with material such as SUS316, and is formedinto a cylinder having a flange 8 a at one end thereof. One end of thecylinder on a side opposite to the flange 8 a is press-fitted and weldedto one end of the outer circumference of the fixed core 1; on the otherhand, the flange 8 a is press-fitted and welded to an annular step (anannular groove) 18 c formed at the inner edge of the upper end of thenozzle body 18. Such welding is performed over the entire couplingboundary of, for example, portions designated by reference characters(b) and (c) by laser welding in order to keep sealability.

Here, the annular step 18 c is a part having the greatest inner diameterof the stepped inner circumference of the nozzle body 18.

An upper portion 18 b of the nozzle body 18 has greatest inner andouter-diameters in the nozzle body 1 in order to house therein themovable core 14 a, described later, in such a manner as to allow afreely reciprocating movement (a stroke movement required for opening orclosing a valve). A slender, long nozzle portion 18 a extends from thelower portion.

In an injection system in which the fuel injector 100 is mounteddirectly in a cylinder head 106 of an engine 105, as shown in FIG. 2,the long nozzle portion 18 a enables an injector body having a largediameter to be placed at a position apart from (i.e., a position withoutany interference with) a suction valve 101, a drive mechanism 102 for asuction/exhaust valve, a intake manifold 103 or the cylinder head 106 inthe case where the suction valve 101, the drive mechanism 102, theintake manifold 103 and the like are mounted at a high density, with anattendant advantage of the higher degree of fixing freedom.

The upper portion (the large-diameter portion) 18 b of the nozzle body18 extends upward to a position at which a magnetic flux for attractingthe movable core is allowed to pass when the electromagnetic coil 2 isenergized, that is, to a position at which a part of the magneticcircuit is constituted. In view of this, the upper portion 18 b of thenozzle body 18 also serves as a part of the yoke 4.

The upper end-surface of the nozzle body 18 includes the above-describedannular step 18 c for allowing the flange 8 a of the seal ring 8 to bepress-fitted thereto while a step 18 d to be press-fitted in a spigotjoint manner to (i.e., in uneven engagement with) the yoke 4, andtherefore, includes three stepped surfaces in total.

In the yoke 4, an opening at the lower end (i.e., one end facing thenozzle body 18) is formed slightly larger than the outer diameter of theelectromagnetic coil 2 with a resin mold 3, and thus, is formed into aso-called drop-bottomed shape. At the lower end of the yoke is formed astep 4 c to be press-fitted to the step 18 d of the nozzle body 18 inthe spigot joint manner.

In the yoke 4, an upper wall 4 b (hereinafter referred to as a shoulder)is formed in such a manner as to cover the upper end of the resin mold 3of the electromagnetic coil 2. At the center of the shoulder 4 b, a coreinserting hole 4 a engageable with the outer circumference of the fixedcore 1 is formed by drawing.

The yoke 4 configured as described above is disposed from above thefixed core 1. Furthermore, the yoke 4 is configured such that it can bepress-fitted (coupled) to the annular step 18 d of the nozzle body 18.inthe spigot joint manner in such a manner as to cover the electromagneticcore 2 with the resin mold 3. At a part of the shoulder 4 b of the yoke4 is formed as a window 4 d, through which a connector terminal 29 forthe electromagnetic coil 3 can be inserted.

The electromagnetic coil 2 is received at the upper end surface of thenozzle body 18, and then, is pressed at the inner surface of theshoulder 4 b of the yoke 4, to be thus fixed thereto.

The yoke 4 and the nozzle body 18 are annularly welded to each other ata jointed portion (a) of the press-fitted portion (i.e., thespigot-jointed portion) therebetween, and further, the yoke 4 and thefixed core 1 are welded to each other at a position (d), thereby keepingthe sealability.

The fixed core 1, the yoke 4, the needle 5 and the nozzle body 18 aremade of, for example, a stainless-based magnetic material (i.e.,electromagnetic stainless) in order to constitute the magnetic circuitof the electromagnetic coil 2. Its machining mode will be describedlater.

At the lower end (i.e., the tip) of the nozzle body 18 are disposed anorifice plate 19 and a fuel swirler (hereinafter simply referred to as aswirler) 21, wherein these component parts 18, 19 and 21 are formed ofseparate members.

The orifice plate 19 is formed by, for example, a stainless-baseddisk-like chip, and is provided at the center thereof with an injectionorifice (an orifice) 20, upstream of which the valve seat 31 is formed.The orifice plate 19 is press-fitted to the inner circumference 18 f ofthe lower end of the nozzle body 18.

In the meantime, the swirler 21 is loosely fitted to the innercircumference of the lower end of the nozzle body 18, and is made of asintered alloy such as SUS416.

The swirler 21 is formed by a substantially disk-like chip, and isprovided at the center thereof with a center hole (a guide) 25 forslidably guiding the tip (the valve element) of the needle 5 and at theupper surface thereof with a guide groove 24 for guiding fuel toward theouter circumference, as shown in FIGS. 4( a) and 4(c).

Moreover, as shown in FIGS. 4( b) and 4(c), an annular step (an annularpassage) 23 is formed at the peripheral edge of the lower surface of theswirler 21, and further, a plurality of, for example, six passagegrooves 26 for forming a fuel swirl are arranged between the annularpassage 23 and the center hole 25. The passage groove 26 is formed insubstantially the tangential direction from the outer diameter of theswirler 21 to the inner diameter thereof, so as to generate swirlingforce in the fuel injected from the passage groove 26 toward the lowerend of the center hole 25.

The annular step 23 is formed because it need serve as a fuel sump.Moreover, a plurality of chamfers 27 are formed at the outercircumference of the swirler 21. The chamfers 27 are referred to inmachining the grooves 24 and 26 and the like.

At the tip (one end on the fuel injection side) of the nozzle body 18 isformed the inner circumference (the stepped inner circumference) 18 fwith a receiving surface 18 e for receiving the swirler 21 and theorifice plate 19. The swirler 21 is received at the receiving surface 18e of the nozzle body 18, to be loosely fitted to the inner circumferenceof the nozzle body. On the other hand, the orifice plate 19 ispress-fitted and welded to the inner circumference in such a manner asto press the swirler 21.

The swirler 21 and the orifice plate 19 are disposed in theabove-described manner, so that the swirler 21 can be held between thereceiving surface 18 e and the orifice plate 19, and further, an annularfuel passage 22 is defined between the outer circumference of theswirler 21 and the inner circumference of the tip of the nozzle body 18.The annular fuel passage 22 can be sufficiently secured as a fuelpassage without any chamber 27. Via these annular fuel passages 22 and23, the fuel can flow into the groove 26 for forming a swirl in theswirler 21.

The upper surface of the swirler 21 is configured such that the fuelguide groove 24 is formed for the purpose of the press-contact with thereceiving surface 18 e formed in the nozzle body 18, so that the fuelstaying upstream of the swirler can flow into the annular fuel passage22 around the swirler 21 via the groove 24. The groove 24 may be formedon a side of the receiving surface 18 e of the nozzle body other thanthe upper end surface of the swirler 21.

That is, whichever the swirler 21 and the nozzle body 18 may be, it issufficient that a passage groove for guiding the fuel around the swirleris defined between the upper end surface of the swirler and thereceiving surface of the nozzle body receiving the former.

Incidentally, a part of the orifice plate 19 intrudes into the groove 26formed at one end surface of the swirler 21 to such an extent that thepart cannot interfere with the flow in the passage groove, and thus,secures the function of a detent of the swirler 21.

For example, if the hardness of the swirler 21 is made to be greaterthan that of the orifice plate 19, a part of the orifice plate 19 canbite the groove 26 when the orifice plate 19 is press-fitted, therebysecuring the detent of the swirler 21 and preventing any misalignment ofthe swirler 21.

The needle 5 includes a valve rod (i.e., a needle) 16 and the hollow,cylindrical movable core 14 having an outer diameter greater than thatof the valve rod 16. The valve rod 16 and the movable core 14 areconstituted of separate members, and are integrally coupled to eachother by press-fitting and welding the valve rod 16 to one end of themovable core 14.

A part of each of the movable core 14 and the valve rod 16 serves as aguide surface on a movable side. Here, one-part 14 a at the outerperipheral surface of the movable core 14 is slidably guided on theinner circumference of the seal ring 8 during a stroke movement at thetime of the valve opening or closing, and then, the peripheral surfacenear the tip of the valve rod 16 is slidably guided to the center hole25 of the swirler 21, thereby constituting a so-called two-point supportguide system.

In the present embodiment, the diameter of the outer circumference 14 aof the upper portion of the movable core 14 is made to be greater thanthat of an outer circumference 14 b of the lower portion thereof, sothat the outer circumference 14 a of the upper portion is slidablyguided at the inner circumferential surface of the seal ring 8; in themeantime, the diameter of the outer circumference 14 b of the lowerportion is made to be smaller than that of the outer circumference 14 aof the upper portion, so that a sufficient fuel passage 13 can besecured between the outer circumference 14 b of the lower portion andthe inner circumference of the nozzle body 18.

The fuel passage 13 and the inside of the movable core 14 serving as anupstream passage 12 communicate with each other via a plurality ofthrough holes (i.e., orifices) 15 formed on a core wall of the outercircumference 14 b of the lower portion.

A step 14 c is formed at the inner surface of the upper portion of themovable core 14, and is provided with an annular plate spring (i.e., adamper plate) 50.

As shown in FIG. 5, the plate spring 50 is formed into an annular shape,and an inside portion designated by reference numeral 51 is punched. Aplurality of elastic pieces 52 projecting inward are formed by punchingin arrangement at equal intervals in the circumferential direction.

The elastic pieces 52 in the plate spring 50 receive one end of acylindrical movable mass (i.e., a weight) 9, which is, for example, acarbon steel forging product.

The movable mass 9 is positioned over one end of the inner circumferenceof the fixed core 1 and one end of the inner circumference of themovable core 14. A hollow hole 11 of the fixed core 1 serves as a fuelpassage. Inside the hollow hole 11 are contained the movable mass 9, thereturn spring 7 and a spring presser 6 in order from under. A filter 30is disposed at the upper end of the hollow hole 11.

The spring presser 6 is fixed by caulking a peripheral portion 10 of thefixed core 1.

The movable mass 9 is interposed between the return spring 7 and theneedle 5 (the movable core 14) in such a manner as to be freely moved inan axial direction independently of the needle 5. In order to ensure theindependent movability, the spring plate 50 is interposed between themovable mass 9 and the needle 5, so that the elastic pieces 52 of thespring plate 50 receive the movable mass 9.

In this manner, the movable mass 9 fulfills a damper function ofsuppressing a bounce of the needle 5 during a valve closing movementowing to its independence of the needle 5 with a valve. This damperfunction produces a remarkably effective result, the principle of whichis considered as follows: namely, it is considered that although theneedle 5 is about to bounce when the needle 5 collides against the valveseat 31 by the force of the return spring 7 during the valve closingmovement, the inertia of the movable mass 9 and the resilientdeformation of the spring plate 50 absorb kinetic energy of the bounceat that time, thereby attenuating the bounce.

A connector mold (i.e., a resin mold) 27 is formed around a portionprojecting from the yoke 4, of the fixed core 1.

Subsequently, a description will be given of the assembly and themachining mode of main component parts in the present embodiment.

As shown in FIG. 3, in assembling the fuel injector in the presentembodiment, the component parts are inserted from above in reference tothe nozzle body 18 except for resin molding with the connector mold.

Pre-processes before assembling the component parts will be explainedbelow.

The yoke 4 is a pressed and cut product. The nozzle body 18 is a coldforged product through not cutting but lathing. The swirler 21 is asintered product through cutting. The orifice plate 19 is lathed, andfurther, is quenched in order to enhance its hardness. The valve seat 31and the orifice 20 are ground and end-lapped.

The valve rod 16 is quenched, and the movable core 14 is annealed.Thereafter, these component parts 14 and 16 are integrally coupled toeach other by press-fitting and welding, thus constituting the needle 5.

The outer circumference of the needle 5 is ground. The outer peripheralsurface (the movable guide surface) 14 a at the upper portion and theend surface (the movable stopper surface) in the movable core 14 aresubjected to hard plating.

The fixed core 1 is a cold forged product through lathing and annealing,and further, the tip thereof serving as a stopper surface with respectto the needle is subjected to hard plating. The seal ring 8 is lathed,and then, is press-fitted and welded to one end of the outercircumference of the fixed core 1 after plating.

The swirler 21 is loosely fitted to the nozzle body 18 by the use of acentering jig, and thereafter, the orifice plate 19 is press fitted andwelded to the nozzle body 18.

The above pre-processed component parts are assembled in the followingprocedure.

The needle 5 having the plate spring 50 disposed therein is insertedinto the nozzle body 18 from above, and then, the flange at one end ofthe seal ring 8 fixed to the fixed core 1 with the seal ring 8 ispress-fitted and welded to the nozzle body 18, so that the fixed core 1and the nozzle body 18 are integrally coupled to each other. Before theintegral coupling, the step of the nozzle body 18 serving as the coupled(press-fitted) portion is measured, and further, the step of the flangeof the seal ring 8 on the side of the fixed core 1 is measured. Thefixed core 1 and the nozzle body 18 through the measurement examinationare integrally coupled to each other. Consequently, the coaxial accuracycan be ensured.

Thereafter, the assembly of the electromagnetic coil 2 and the yoke 4are fitted into the fixed core 1 from above. The yoke 4 is also coupledto the nozzle body 18 by press-fitting and welding. And then, theconnector mold 27 is formed.

The above finished products constitute the magnetic circuit, describedalready, when the electromagnetic coil is energized (excited), so thatthe needle 5 is attracted until it abuts on one end of the fixed core 1against the force of the return spring 7, thereby achieving the valveopening movement. At the time of the valve opening, pressurized fuel isinjected with a swirl from the injection orifice 20 via the swirler 21through the filter 30, the fuel passages 11 and 12, the orifices 15 andthe passages 13 and 17.

The present embodiment can produce the following effects:

(1) When the electromagnetic coil 2 is de-energized, the needle 5 ismoved in the closing direction by a load accumulated in the returnspring 7, and then, abuts against the valve seat 31. At this time, thedamper function of the movable mass 9 and the plate spring 50, asdescribed already, suppresses the bounce of the valve element 16,thereby effectively preventing any secondary injection.

(2) Furthermore, since the entire outer circumference 14 a of the upperportion of the movable core is slidably guided on the innercircumference of the seal ring 18 during the valve opening/closingmovement, the fuel is hardly relieved to the slidably guiding surface,and consequently, all the fuel flows between the passage 12 inside ofthe movable core 14 and the passage 13 outside thereof via the orifices15. Therefore, the liquid damper function is appropriately fulfilledbetween the lower end surface (the stopper) of the fixed core 1 and theend surface of the movable core 14, thus contributing to alleviation ofan impact of the needle 5 with respect to the stopper and suppression ofthe bounce of the needle 5 at the time of the valve closing.

(3) The needle 5 is supported and guided at the two points on the innercircumference of the swirler 21 and the inner circumference of the sealring 8. Consequently, the nozzle body per se need not be equipped with aguide function, unlike the prior art. Therefore, it becomes unnecessaryto grind the nozzle body with high accuracy while the seal ring, whichis easy to be lathed, can ensure the highly accurate guide function.Thus, the needle can be supported and guided at the two points at areduced cost even in the case of a long nozzle injector.

(4) The prior art has experienced the problem that the coaxial accuracyis enhanced while eliminating a troublesome grinding work (the guideformation) with respect to the inner circumference of the nozzle body18. However, through the above-described assembling process, the fixedcore 1 and the nozzle body 18 can be integrally coupled to each other bypress-fitting and welding the seal ring 18 with relative facilitationwhile the high coaxial accuracy is maintained, thereby streamlining theassembling work and reducing the cost.

(5) Moreover, as shown in FIG. 3, all of the component parts except theconnector mold can be assembled in the same direction in reference tothe nozzle body 18, thus contributing to the facilitation and automationof the work.

(6) Since the swirler 21 is loosely fitted while is fixed to the orificeplate 19, the swirler 21 can be prevented from being shifted, andfurther, the entire circumference of the swirler 21 constitutes theannular fuel passage, thereby reducing passage resistance, facilitatingthe relief of bubbles, which have been liable to remain at the lower endof the swirler 21, and achieving the smooth fuel injection.

(7) Although the swirler 21 is loosely fitted, it is free from physicalrestriction of other members until the centering jig is set in fitting,thereby offering the degree of centering freedom. Furthermore, even inthe case where the orifice plate 19 is welded, thermal expansion causedby the resultant welding heat also is absorbed at the clearance definedaround the swirler 21, thus preventing any generation of thermaldeformation in the swirler 21.

(8) The annular passage 23 defined by the annular step is formedupstream of the groove 24 for forming the fuel swirl at the lower endsurface of the swirler 21, and thus, functions as the fuel sump.Consequently, it is possible to enhance the injection responsiveness atthe time of the fuel injection.

INDUSTRIAL APPLICABILITY

As described above, the present invention can solve the problems so asto reduce the cost of the fuel injector, enhance the centering accuracy(the coaxial accuracy), facilitate the assembling work, simplify thecomponent parts, offer the degree of fixing freedom, prevent anysecondary injection and the like.

1. An electromagnetic fuel injector, in which a hollow fixed core, anelectromagnetic coil and a yoke are arranged from the center toward theouter diameter, a needle with a valve element is contained in a nozzlebody fixed to the lower portion of the yoke, and the needle is urgedtoward a valve seat by the force of a return spring, the electromagneticfuel injector characterized in that: a fuel swirler positioned upstreamof an injection orifice is disposed at the tip of the nozzle body, thefixed core and the nozzle body being coupled to each other through anon-magnetic cylindrical seal ring press-fitted and welded to the outercircumference of one end on the nozzle body side of the fixed core andthe inner circumference of one end of the nozzle body; and the innercircumference of the fuel swirler and the inner circumference of theseal ring function as a guide for slidably guiding a stroke movement ofthe needle.
 2. An electromagnetic fuel injector according to claim 1,characterized in that the yoke and the nozzle body also are coupled toeach other by press-fitting and welding.
 3. An electromagnetic fuelinjector according to claim 2, characterized in that the seal ring has aflange at one end thereof, one end of a cylindrical portion on a sideopposite to the flange is press-fitted and welded to one end of theouter circumference of the fixed core, while the flange is press-fittedand welded to an annular step formed at the upper end of the nozzlebody; and the yoke and the nozzle body are press-fitted in a spigotjoint manner, followed by welding.
 4. An electromagnetic fuel injector,in which an electromagnetic coil and a yoke are arranged around a hollowcylindrical fixed core, a nozzle body containing therein a needle with avalve element is fixed to the lower portion of the yoke, and the needleis urged toward a valve seat by the force of a return spring, theelectromagnetic fuel injector characterized in that: the fixed core andthe nozzle body comprise an assembly by being united through anon-magnetic cylindrical seal ring; the electromagnetic coil and theyoke are arranged to be passed over the top of the fixed core andpositioned around the fixed core; the yoke is coupled to the upper endof the nozzle body in such a manner as to cover the top of theelectromagnetic coil; a terminal taking-out window for theelectromagnetic coil is formed at a part of the upper portion of theyoke; and the inner surface of the upper end of the yoke presses theelectromagnetic coil, thereby the coil is fixed between the outersurface of the assembly and the inner surface of the yoke.
 5. Anelectromagnetic fuel injector according to claim 4, characterized inthat an inner circumference of the upper end of a bore of the yokethrough which the fixed core passes is coupled to the outercircumference of the fixed core by any of welding, press-fitting andcaulking.
 6. An electromagnetic fuel injector, in which anelectromagnetic coil and a yoke are arranged around a fixed core, anozzle body containing therein a needle with a valve element is fixed tothe lower portion of the yoke, and the needle is urged toward a valveseat by the force of a return spring, the electromagnetic fuel injectorcharacterized in that: the fixed core and the nozzle body are coupled toeach other through a non-magnetic cylindrical seal ring extending overthe outer circumference of one end of the fixed core and the innercircumference of one end of the nozzle body; the inner circumference ofthe seal ring serves as a guide for the needle; the needle has a hollow,cylindrical movable core, the outer circumference of the upper portionof the movable core being slidably guided on the inner circumference ofthe seal ring during a stroke movement, a fuel passage being securedbetween the outer circumference of the lower portion and the innercircumference of the nozzle body, and the fuel passage communicatingwith another fuel passage defined inside of the movable core via athrough hole formed at the movable core.
 7. An electromagnetic fuelinjector according to claim 6, characterized in that the outercircumference of the lower portion of the movable core is made to besmaller in diameter than the outer circumference of the upper portionthereof so as to enlarge the fuel passage defined between the outercircumference of the lower portion and the inner circumference of thenozzle body, the through hole being formed on a core wall on which theouter circumference of the lower portion is positioned.
 8. Anelectromagnetic fuel injector characterized in that: a nozzle body, anorifice plate having an injection orifice and a fuel swirler are formedof separate members; an inner circumference having a receiving surfacefor disposing the fuel swirler and the orifice plate is formed at oneend on a fuel injection side of the nozzle body; the fuel swirler is isput in the inner circumference of the nozzle body with a clearance insuch a manner as to be received at the receiving surface of the nozzlebody; and the orifice plate is fitted and welded to the innercircumference in such a manner as to press the fuel swirler on thereceiving surface, thereby the fuel swirler and the orifice plate areset into one end of the nozzle body in order of the fuel swirler,followed by the orifice plate.
 9. An electromagnetic fuel injectorcharacterized in that: a nozzle body, an orifice plate having aninjection orifice and a fuel swirler are formed of separate members; aninner circumference having a receiving surface for disposing the fuelswirler and the orifice plate is formed at one end of a fuel injectionside of the nozzle body; the fuel swirler and the orifice plate are setinto one end of the nozzle body in order of the fuel swirler, followedby the orifice plate; and the fuel swirler is held by the receivingsurface of the nozzle body and the orifice plate, thereby an annularfuel passage is formed between the outer circumference of the fuelswirler and the inner circumference of the nozzle body, so that fuelflows into a passage groove formed at the lower end surface of the fuelswirler via the annular fuel passage.
 10. An electromagnetic fuelinjector characterized in that: a nozzle body, an orifice plate havingan injection orifice and a fuel swirler are formed of separate members,an inner circumference having a receiving surface for disposing the fuelswirler and the orifice plate is formed at one end on a fuel injectionside of the nozzle body, the fuel swirler is loosely fitted to the innercircumference of the nozzle body in such a manner as to be received atthe receiving surface of the nozzle body, the orifice plate ispress-fitted and welded to the inner circumference in such a manner asto press the fuel swirler, and a guide groove for guiding the fuel tothe outer circumference of the fuel swirler is formed between the upperend surface of the fuel swirler and the receiving surface of the nozzlebody for receiving the upper end surface of the fuel swirler.
 11. Anelectromagnetic fuel injector according to claim 10, characterized inthat the guide groove is formed at the upper end surface of the fuelswirler and/or the receiving surface of the nozzle body.
 12. Anelectromagnetic fuel injector characterized in that: a nozzle body, anorifice plate having an injection orifice and a fuel swirler are formedof separate members, an inner circumference having a receiving surfacefor disposing the fuel swirler and the orifice plate is formed at oneend on a fuel injection side of the nozzle body, the fuel swirler isloosely fitted to the inner circumference of the nozzle body in such amanner as to be received at the receiving surface of the nozzle body,the orifice plate is press-fitted and welded to the inner circumferencein such a manner as to press the fuel swirler, and the hardness of thefuel swirler is greater than that of the orifice plate.
 13. Anelectromagnetic fuel injector characterized in that: a nozzle body, anorifice plate having an injection orifice and a fuel swirler are formedof separate members, an inner circumference having a receiving surfacefor disposing the fuel swirler and the orifice plate is formed at oneend on a fuel injection side of the nozzle body, the fuel swirler isloosely fitted to the inner circumference of the nozzle body in such amanner as to be received at the receiving surface of the nozzle body,the orifice plate is press-fitted and welded to the inner circumferencein such a manner as to press the fuel swirler, and a part of the orificeplate intrudes into the passage groove for generating a swirl, formed atthe lower end surface of the fuel swirler.
 14. An electromagnetic fuelinjector in which a fuel swirler is disposed upstream of a fuelinjection orifice, the electromagnetic fuel injector characterized inthat: the upper surface of the fuel swirler is equipped with fuelpassage grooves for letting fuel flow from a center of the fuel swirlerto an outer circumference thereof; the lower surface of the fuel swirleris equipped with passage grooves for generating a swirl to fuel and anannular passage communicating with the passage grooves for swirl at anupstream side of the passage grooves; the outer circumference of thefuel swirler is equipped with faces to be fuel passages for connectingthe fuel passage grooves of the upper surface and the annular passage ofthe lower end surface.
 15. An electromagnetic fuel injector according toclaim 14, characterized in that the annular passage is defined byforming an annular step at the peripheral edge of one end surface of thefuel swirler.
 16. An electromagnetic fuel injector, in which a hollowfixed core, an electromagnetic coil and a yoke are arranged from thecenter toward the outer diameter, a needle with a valve element iscontained in a nozzle body fixed to the lower portion of the yoke, andthe needle is urged toward a valve seat with application of the force ofa return spring, the electromagnetic fuel injector characterized inthat: a mass movable in an axial direction independently of the needleis interposed between the return spring and the needle.
 17. Anelectromagnetic fuel injector, in which a hollow fixed core, anelectromagnetic coil and a yoke are arranged from the center toward theouter diameter, a needle having a valve element is contained in a nozzlebody fixed to the lower portion of the yoke, and the needle is urgedtoward a valve seat by the force of a return spring, the electromagneticfuel injector characterized in that: a mass movable in an axialdirection independently of the needle is interposed between the returnspring and the needle, and a plate spring is interposed between the massand the needle.
 18. An electromagnetic fuel injector characterized inthat: a nozzle body, an orifice plate having an injection orifice and afuel swirler are formed of separate members, an inner circumferencehaving a receiving surface for disposing the fuel swirler and theorifice plate is formed at one end of a fuel injection side of thenozzle body, the fuel swirler is held between the receiving surface ofthe nozzle body and the orifice plate, thus defining an annular fuelpassage between the outer circumference of the fuel swirler and theinner circumference of the nozzle body, so that fuel flows into apassage groove formed at the lower end surface of the fuel swirler viathe annular fuel passage, and a guide groove for guiding the fuel to theouter circumference of the fuel swirler is formed between the upper endsurface of the fuel swirler and the receiving surface of the nozzle bodyfor receiving the upper end surface of the fuel swirler.
 19. Anelectromagnetic fuel injector according to claim 18, characterized inthat the guide groove is formed at the upper end surface of the fuelswirler and/or the receiving surface of the nozzle body.